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Black silicon (bSi) is promising for integration into silicon solar cell fabrication flow due to its excellent light trapping and low reflectance, and a continuously improving passivation. However, intensive ion bombardment during the reactive ion etching used to fabricate bSi induces surface damage that causes significant recombination. Here, we present a process optimization strategy for bSi, where surface damage is reduced and surface passivation is improved while excellent light trapping and low reflectance are maintained. We demonstrate that reduction of the capacitively coupled plasma power, during reactive ion etching at non-cryogenic temperature (-20 °C), preserves the reflectivity below 1% and improves the effective minority carrier lifetime due to reduced ion energy. We investigate the effect of the etching process on the surface morphology, light trapping, reflectance, transmittance, and effective lifetime of bSi. Additional surface passivation using atomic layer deposition of Al2O3 significantly improves the effective lifetime. For n-type wafers, the lifetime reaches 12 ms for polished and 7.5 ms for bSi surfaces. For p-type wafers, the lifetime reaches 800 μs for both polished and bSi surfaces. [ABSTRACT FROM AUTHOR]

The influence of the SiOxFy selfmasking process on the formation of black-Silicon (b-Si) textures by maskless SF6/O2 plasma etching is of great interest with regard to the optimization of the texturing process for highly antireflective silicon. For that reason, the elemental composition of plasma textured silicon surfaces is analyzed by transmission electron microscopy and X-ray photoelectron spectroscopy. The chemical composition of a fluorine containing oxide layer on top of the surface was confirmed and determined quantitatively. A strongly reduced F content was found after ambient air exposure. A qualitative model of the chemical and physical processes caused by maskless plasma texturing was developed to explain the observed experimental results. The decrease in the F content is assumed to be caused by hydrolysis of F by air moisture, resulting in a successive desorption of HF and transformation of SiOxFy to silicon oxide. [ABSTRACT FROM AUTHOR]

Potential-induced degradation (PID) can cause massive power losses in photovoltaic power plants with serially connected modules when high electrical potential between solar cells and the module front glass surface leads to shunting of Si solar cells. The shunting is reversible to a large extend through elevated temperatures and/or by application of reversed voltages. It was previously shown that PID-related shunting (PID-s) of the p-n junction occurs due to Na-decorated stacking faults in {111} planes. Defects at former PID-shunt positions that have been thermally 'healed' (recovered) do not show a Na decoration anymore. In this contribution we investigate stacking faults with Na decoration and with vanished Na decoration after thermal recovery. HAADF STEM imaging is used for principal investigation of the atomic structure of PID-s defects. The Na decorated stacking fault appears as a dark region in the HAADF STEM image. By contrast, the atomic structure of the recovered stacking fault can be clearly imaged. The orientation of Si dumbbells indicates an extrinsic stacking fault that remains after recovery by Na out-diffusion. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

ABSTRACT Multicrystalline solar cells break down strongly at reverse voltages well below the theoretical limit. Previous explanations were based on assuming a constant depth of the junction below the surface. In this work, preferred phosphorous diffusion at special line defects in grain boundaries is shown to lead to spikes in the p-n junctions even below flat surfaces. The curvature radii of the spherical p-n junction bending are measured by electron beam-induced current to be in the range of 300-500 nm, leading to the observed type III avalanche breakdown voltages. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Potential‐induced degradation (PID) of photovoltaic solar modules gained a lot of interest during the last three years. Many PID‐affected modules based on crystalline silicon show intense shunting of the solar cells. In the past, character and origin of these PID‐shunts have not been clear. In the contribution by Naumann et al. (see pp. 315–318) monocrystalline and multicrystalline silicon solar cells have been prepared with PID of the shunting type. In plan view, SEM using electron beam induced current and secondary ion mass spectrometry measurements reveal local PID‐shunts correlated with sodium accumulations. Detailed TEM investigations at cross sections of PID‐shunts reveal stacking faults in silicon decorated with sodium. It is concluded that the sodium decorated stacking faults provide paths with high conductivity across the p–n junction, thus leading to the observed shunting. [ABSTRACT FROM AUTHOR]